Just an addendum to my post about the WKRP package being shown on WGN America: if WGN gets to the later seasons, you'll notice that while there are still some horrendous music changes ("Hold My Order, Terrible Dresser"), there is actually a lot of real music left in, including some pretty expensive stuff like the Beatles, the Who, and various groups with Stone and/or Stones in the title. By the final season, most of the music is intact.
The fact that a lot of music was left in probably wasn't due to any sudden attack of integrity on the part of MTM; it's that as the show went on, more and more scenes were done with music underscoring them all the way. In the first season, the DJ would usually turn off the music just after it started playing, unless it was a scene specifically built around the music like the Pink Floyd scene. But in the later episodes, they just used the songs as kind of a built-in underscore. Here's an example of what I'm talking about: Johnny puts on "Come Together" by the Beatles, announces it, and then lets the song play under the ensuing scene. Most episodes do not have separate music/dialogue tracks, so there are only two choices: pay for the music, or cut a minute and a half from the episode.
This may be another reason why Fox dropped the idea of further DVD releases; they just about got by with the first season because enough buyers were willing to overlook the cut music for the sake of the comedy, but in subsequent seasons, a lot of long scenes have music that can't be removed.